shark species

SHARK SPECIES INFORMATION

Great Hammerhead

Great Hammerhead, Sphyrna mokarran

The IUCN has classified the Great Hammerhead shark as 'Globally Endangered.'

Status

The Great Hammerhead is specifically vulnerable to over-exploitation due to its high sensitivity to stress and low reproductive rate. When caught as by-catch in pelagic longline, bottom longline, and net fisheries, it has at least a 90% mortality rate.

With uniquely large dorsal and caudal fins, the Great Hammerhead is also being hunted to extinction for its fins. The demand for fins has increased in the past few decades due to the popularity of shark fin soup, especially in Asian markets. Prices have risen above US$50/lb in species-dense areas such as Central America.

As a solitary animal, the Great Hammerhead is not known to have large populations in any one specific area. But reported data from the Atlantic and Indian Oceans suggest an overall decline of 50-90% in the past three decades. One significant obstacle to accurate population surveys is the mistaken identity for other species of Hammerhead sharks. Further population data need to be collected in order to create effective protection and enforcement. Although some fishing states such as the U.S. and Australia have adopted shark finning bans, the majority of the industry is highly unregulated.

Habitat & Ecology

Hammerhead Habitat & Ecology

The Great Hammerhead has a preference toward warmer water and thus can be found primarily in tropical and semi-tropical regions. As a coastal-pelagic and semi-oceanic species, it ranges in location from close inshore and offshore waters to continental shelves, island terraces, and even depths over 80m.

Maximum total lengths exceed 600cm, but mature adults commonly measure 400cm. This elusive species does not have a well-known life span, but some biological cycles are documented. Females typically breed every other year, giving birth to 6-42 pups in late spring after an 11-month gestation period.

It has a highly varied diet, consisting of invertebrates (i.e. squid, octopus), bony fish (i.e. sardine, jack, grouper, toadfish, etc.), smaller sharks (i.e. smoothhounds), rays and skates. One interesting feeding behavior is that the shark uses its 'hammer,' or cephalofoil, to pin down stingrays against the ocean floor while biting off the pectoral fins, before consuming the rest of the ray.

Information and direct verbiage sourced from:

Denham, J., Stevens, J., Simpfendorfer, C.A., Heupel, M.R., Cliff, G., Morgan, A., Graham, R., Ducrocq, M., Dulvy, N.D, Seisay, M., Asber, M., Valenti, S.V., Litvinov, F., Martins, P., Lemine Ould Sidi, M., Tous, P. and Bucal, D. 2007. Sphyrna mokarran. In: IUCN 2010. IUCN Red List of Threatened Species. Version 2010.3. www.iucnredlist.org. Downloaded on 10 December 2010.

Hammerhead Photo by Neil Hammerschlag.

*All maps are courtesy of the IUCN Red List.

Bull Shark

Bull Shark, Carcharhinus leucas

The IUCN has classified the Bull Shark as 'Near Threatened Globally.'

Status

Due to its unique ability to withstand highly variable salinities ranging from hypersaline to virtually freshwater, Bull Sharks have a high likelihood of human contact in inter-coastal ecosystems. Both commercial and recreational fisheries exploit the Bull Shark for its skin, liver oil, flesh, and fins. In the Gulf of Mexico, the Bull Shark has been known to make up 11% of the recreational shark catch. Similar to the Great Hammerhead, the demand for shark fin soup has also dramatically increased commercial fishing pressure on this species.

The other primary threats to Bull Shark populations are pollution and habitat modification. Its nursery locations are typically in estuarine and freshwater systems, which are often in close proximity to human settlements and their pollutants. Unnaturally warm water is both a pollutant and form of habitat modification. In Florida, the warm water that flows from the power stations, such as Turkey Point, confuses the juvenile sharks into staying local in the winter instead of migrating south to warmer waters, as its normal behavior would suggest.

Currently, no comprehensive conservation or management of the Bull Shark exists. In the U.S., it is considered part of the 'large coastal' group, which has a quota of 1,285 ton/year. Juvenile Bull Sharks, however, have benefited in the U.S. from recent gillnet bans in coastal waters.

Habitat & Ecology

Hammerhead Habitat & Ecology

With a total length of about 340cm, the Bull Shark does not grow as long as the Great Hammerhead. It is, however, a highly muscular animal with strong hunting capabilities. Its diet is known to consist of turtles, birds, dolphins, terrestrial mammals, crustaceans, echinoderms, teleost fishes, and elasmobranchs. The larger the individual, the more diverse its prey options.

Information and direct verbiage sourced from:

Simpfendorfer, C. & Burgess, G.H. 2005. Carcharhinus leucas. In: IUCN 2010. IUCN Red List of Threatened Species. Version 2010.3. www.iucnredlist.org. Downloaded on 05 October 2010.

Bull Shark Photo by Klaus Jost, Courtesy of the Florida Museum of Natural History.

*All maps are courtesy of the IUCN Red List.

Tiger Shark

Tiger Shark, Galeocerdo cuvier

The IUCN has classified the Tiger Shark as 'Near Threatened Globally.'

Status

As with both the Great Hammerhead and Bull Sharks, the Tiger Shark is subject to great fishing pressure for its fins. In addition, Tiger Shark flesh is among the lowest in mercury content; thus it is sought after for flesh, skin, liver oil, and cartilage. Very few records exist of commercial fishery catch loads, but observer data are often used for population estimates. In the U.S., the Tiger Shark is the third most common large, coastal species, accounting for 12-20% of the catch; however, only 5% of the landed catch is Tiger Shark, perhaps due to released juvenile by-catch. In tuna and swordfish longline fisheries, Tiger Sharks are often significant by-catch, especially when operated on or near the continental and insular shelves.

With the fierce reputation that Tiger Sharks have gained over previous years, shark control programs in tropical regions such as Queensland and Hawaii are focusing on target elimination of this species in areas with high attack rates. The evidence is conflicting over the efficacy of these programs, with data pointing toward steady or even increased concentrations in netted areas.

The final primary threat to the Tiger Shark is mortality from human garbage ingestion. Nicknamed the 'garbage disposal,' it has a high propensity to consume plastics, metal, bags, scraps, and virtually any other discarded item floating in the ocean.

No specific protection of the Tiger Shark exists. As with the Bull Shark, the Tiger Shark is categorized in the U.S. as part of the 'large coastal' group with an annual quota of 1,285 ton/yr.

Habitat & Ecology

Hammerhead Habitat & Ecology

The Tiger Shark range is relatively large, covering both tropical and temperate seas. It has the highest concentrations, however, in warm waters. Little is known about its depth range, though one study recorded an individual at 350m below the surface.

As suggested by the Tiger Shark's final threat, garbage consumption, this species is known to have the most diverse diet of any shark. Natural prey includes bony fish, sharks, rays, turtles, sea birds, seals, dolphins, sea snakes, cephalopods, crabs, lobsters, gastropods and jellyfish.

The growth rate of individual sharks is estimated to be initially rapid but later tapers off to 5-10cm/yr. Thus, an individual with a total length of 400-450cm would be around 20-25 years old. Its maximum age is estimated to be about 45-50 years. Although female gestation period is estimated to be 13-16 months, the average litter size is relatively large, with an average of 30-35 pups.

Information and direct verbiage sourced from:

Simpfendorfer, C. 2005. Galeocerdo cuvier. In: IUCN 2010. IUCN Red List of Threatened Species. Version 2010.4. www.iucnredlist.org. Downloaded on 09 December 2010.

Tiger Shark Photo by Neil Hammerschlag.

*All maps are courtesy of the IUCN Red List.